eval { 
     local $SIG{ALRM} = sub { die "alarm\n" }; # NB: \n required 
   alarm($timeout);
   #
   # do stuff that might time out
   #

   alarm 0;
};
if ($@) {
    die unless $@ eq "alarm\n";   # propagate unexpected errors
    # handle the timed out operation
    
} else {
    # operation didn't time out, handle it's result
}